Conventional rotary joints of this kind have a stator fixedly mounted to, for example, the distal end of a robot arm, and a rotor fixedly mounted to a hand side of the robot and rotatably coupled and supported to the stator, and are configured to allow communication of fluid, such as air, cooling water or welding gas, and electricity such as power electricity or electric signals between the stator and rotor so that communication of such fluid and electricity can be established even when the hand side of the robot rotates with respect to the stationary side thereof.
Furthermore, for fluid communication, the above rotary joints employ a swivel joint in which plural kinds of fluid passages are arranged between the slide surfaces of the stator and rotor. For power electricity communication, the above rotary joints employ a power slip ring consisting of a collector ring mounted to one of the stator and rotor and a slide contact mounted to the other for coming into sliding contact with the collector ring to feed electricity.
There are also known electric signal slip rings for passing electric signals between a stator and a rotor. Proposed as an example of such electric signal slip rings is, as disclosed in Japanese Unexamined Patent Publication No. 10-223346, an electric signal slip ring which includes a stationary side electrode of ring plate shape disposed on the stator side, a rotating side electrode of ring plate shape disposed on the rotor side, and a rolling element disposed between both the electrodes, and which is configured to roll the rolling element on both the electrodes by relative rotation of the rotor to the stator to pass electric signals between both the electrodes.
As described above, the rotary joint is provided with a slip ring for transmitting electric power or electric signals between the stator and rotor relatively rotating to each other. When water from the swivel joint or dust from the outside of the rotary joint sticks to the slip ring, however, leakage of electric power or failure in electric signal may occur to cause maloperation of the robot, abnormal wear of the sliding parts and so on. It is therefore desirable to institute some measures against these problems.
The present invention has been made in view of the foregoing points, and therefore its main object is to avoid penetration of water droplets or the like into the surroundings of the slip ring in the rotary joint as described above, thereby preventing the occurrence of electric leakage and so on in the power slip ring.